Methods for producing vinyl phenols from ethyl phenols by their catalytic dehydrogenation in a gaseous phase in the presence of water, benzene or some other diluent such as nitrogen or carbon dioxide gas are known and are described in Japanese Patent Publication Nos. 41183/74 and 43491/78, as well as in Japanese patent application (OPI) Nos. 55529/79, 28958/80 and 203022/82, etc. (The symbol OPI as used herein means an unexamined published Japanese patent application).
In the above known methods, the selectivity for the end product p-vinyl phenol can be increased up to 90 to 95% or higher by employing optimum reaction conditions. However, in industrial operations using large apparatuses, for example, a large fixed bed catalytic reactor, the dehydrogenation of p-ethyl phenol, which is an endothermic reaction, causes fluctuations in the temperature of the catalyst bed or the reactant flow through the catalyst bed. As a result, it has been difficult to maintain optimum conditions throughout the reaction system in industrial operations and the selectivity for p-vinyl phenol has been at most only 80 to 85%.
In addition, the cost of p-ethyl phenol accounts in large part for the overall cost of the production of p-vinyl phenol. Thus, reduction of the loss of p-ethyl phenol, which occurs in industrial operations due to side reactions, has long been desired.